Light emitting device and display apparatus using same

ABSTRACT

There is provided a high light-emission-efficiency, highly stable, low-cost light emitting device that utilizes a copper complex as a light emitting material and comprises a pair of electrodes provided on a substrate, and an organic substance layer provided between the electrode and comprising a metal coordination compound having a partial structure represented by the general formula (1): 
                         
wherein Cu represents a copper ion.

TECHNICAL FIELD

The present invention relates to a light emitting device using an organic compound and more particularly, relates to a light emitting device improved in stability and light emission efficiency by employing a metal coordination compound as a light emitting material.

BACKGROUND ART

The organic EL (electroluminescent) device is being actively subjected to application study as a light emitting device of a high-speed response and a high light emission efficiency. The basic constitution thereof is shown in FIGS. 1A to 1C (see, for example, Macromol. Symp. 125, 1-48 (1997)).

As shown in FIGS. 1A to 1C, an organic EL device is generally composed of a transparent electrode 14 and a metal electrode 11 on a transparent substrate 15, and a plurality of organic film layers disposed between the electrodes.

In FIG. 1A, an organic layer consists of a light emitting layer 12 and a hole transport layer 13. As the material for the transparent electrode 14, a material with a large work function, such as ITO, is used to achieve good hole-injecting characteristics from the transparent electrode 14 to the hole transport layer 13. As the material for the metal electrode 11, a material with a small work function, such as aluminum, magnesium and alloys thereof, is used to achieve good electron-injecting characteristics to the organic layer. These electrodes generally have a thickness of 50-200 nm.

For the light emitting layer 12, an aluminoquinolinol complex (a representative example is Alq shown in FIG. 2) or the like is used. As the hole transport layer 13, for example, an electron-donating material such as a triphenylamine derivative (a representative example is α-NPD shown in FIG. 2) is used.

The organic EL device constructed as described above has a rectifying property, and when an electric field is applied so as to make the metal electrode 11 act as a cathode and the transparent electrode 14 act as an anode, electrons are injected from the metal electrode 11 into the light emitting layer 12, and holes are injected from the transparent electrode 14 into the light emitting layer 12.

When the injected holes and electrons recombine in the light emitting layer 12, excitons are formed to emit light. At this time, the hole transport layer 13 plays the role of an electron blocking layer to raise the recombination efficiency at the light emitting layer 12/hole transport layer 13 interface, and to enhance the light emission efficiency.

Furthermore, in FIG. 1B, an electron transport layer 16 is formed between the metal layer 11 and the light emitting layer 12 of FIG. 1A. Thus, the light emitting function can be isolated from the electron/hole transport function to make the carrier blocking action more effective, thereby improving the light emission efficiency. As the material for the electron transport layer 16, for example, an oxadiazole derivative or the like can be used.

Furthermore, as shown in FIG. 1C, an exciton-diffusion preventing layer 17 is additionally provided in order to confine excitons generated in the light emitting layer 12 within the light emitting layer 12 to effect efficient light emission.

Moreover, it is also possible to constitute an organic EL device with a single layer structure of an organic substance layer. Such a device is generally produced by forming a first electrode on a substrate, then forming a polymer film thereon by a coating method or the like, and forming a second electrode on the top thereof, but can also be produced by vacuum vapor deposition of low-molecular weight compounds.

Further, there are generally used two types of the light emitting layer, that is, a guest-host type wherein a light emitting material is dispersed in a carrier transport material, and another type wherein only a light emitting material is used in 100%. Most light emitting materials, when used in a high concentration in a light emitting layer, are liable to show a decreased light emission efficiency, and in such a case, it is preferable to select a suitable host material to adopt a guest-host type light emitting layer.

In the present invention, copper complex compounds of specific structures are employed as a light emitting material of an organic EL device.

As for the prior art concerning copper complexes, there are techniques using copper complex compounds different from the copper complex compounds employed in the present invention, but there are no disclosure of those copper complex compounds having sufficient performance to be used for display, illumination, or the like.

Examples of the prior art are identified as follows.

-   Document 1: Y. Ma et al., Advanced Materials, 1999, 11, No. 10, p85,     High Luminescence Gold (1) and Copper (1) Complexes with Triplet     Excited State for Use in Light-Emitting diodes -   Document 2: Japanese Patent Application Laid-Open No. 10-308277     (Japanese Patent No. 2940514) to T. Azumaguchi et al.

There is a description therein that copper complexes can be produced at a relatively low cost and sufficiently drawing the performance of copper complexes makes it possible to provide low-cost, high-performance organic EL devices.

However, because EL devices obtained in the above documents have extremely low light emission efficiencies, and because there is no sufficient description in the above documents of the efficiencies of the devices, it is not believed that the characteristics of copper complexes were sufficiently drawn.

DISCLOSURE OF THE INVENTION

It is, therefore, an object of the present invention to provide a high light-emission-efficiency, highly stable, low-cost light emitting device.

In the light emitting device in accordance with the present invention, there are employed as a light emitting material copper complex compounds, which include not only known compounds but also novel compounds.

According to the present invention, there is provided a light emitting device comprising a pair of electrodes provided on a substrate, and an organic substance layer provided between the electrode and comprising a metal coordination compound having a partial structure represented by the general formula (1):

wherein Cu represents a copper ion, and heterocyclic ring A including nitrogen atom N represents a pyridine or quinoline ring, or a heterocyclic ring having one or more C—H of a pyridine or quinoline ring replaced with nitrogen atom(s), and the heterocyclic rings may have a substituent selected from the group consisting of an aromatic ring group that may have a substituent, a halogen atom, or a linear or branched alkyl group having 1 to 10 carbon atoms in which only a single methylene group or two or more non-adjacent methylene groups of the alkyl group may be substituted with —O—, —S—, —CO—, —CO—O—, —O—CO—, —CH═CH—, or —C≡C—, and a hydrogen atom of the alkyl group may be substituted with a fluorine atom or an aromatic ring group.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are views each illustrating a constitution of an ordinary light emitting device;

FIG. 2 is a view illustrating chemical structures of ordinary electron transport materials and hole transport materials;

FIG. 3 is a view illustrating monodentate ligands having an aromatic ring imine structure that can be utilized for copper complexes of the present invention, the nitrogen atom of which coordinates with copper (Cu);

FIG. 4 is a view illustrating bidentate ligands having a bipyridine structure that can be utilized for copper complexes of the present invention, the two nitrogen atoms of the bipyridine of which coordinates with copper (Cu);

FIG. 5 is a view illustrating bidentate ligands having a phenanthroline structure that can be utilized for copper complexes of the present invention, the two nitrogen atoms of which coordinates with copper (Cu);

FIG. 6 is a view illustrating bidentate ligands having a 2-phenylpyridine structure that can be utilized for copper complexes of the present invention, which coordinates with copper (Cu) at position 2 of each of the pyridine and phenyl;

FIG. 7 is a view illustrating bidentate ligands having a benzoquinoline structure that can be utilized for copper complexes of the present invention, the nitrogen and carbon of the rings of which coordinates with copper (Cu);

FIG. 8 is a view illustrating bidentate ligands having a bipyridine derivative structure that can be utilized for copper complexes of the present invention;

FIG. 9 is a view illustrating bidentate ligands having a 2-phenylpyridine derivative structure that can be utilized for copper complexes of the present invention;

FIG. 10 is a view illustrating other monodentate or bidentate ligands that can be utilized for copper complexes of the present invention, in which PPh3 (1001) is a monodentate ligand and coordinates with copper (Cu) at the phosphorus (P), and the others are bidentate ligands and coordinate with copper (Cu) at the oxygen (O), nitrogen (N), and phosphorus (P);

FIG. 11 is a view illustrating another ligand 1101 that can be utilized for copper complexes of the present invention, which is a tridentate ligand and coordinates with copper (Cu) at the three nitrogen atoms);

FIG. 12 is a view showing examples of copper complex compounds employed in the present invention;

FIG. 13 is a view showing the structure of a polymer copper complex employed in the present invention; and

FIG. 14 is a graphical representation showing a light emission spectrum of the light emitting device of Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION

The copper complexes employed in the present invention is mainly characterized in that the copper ion as a metal center is in +1 charge state. For the electron configuration of a copper atom, a copper ion of +1 charge has 10 d-electrons. The present inventors' experience shows that most transition metals having an even number of d-metals exhibit good light emission characteristics. As copper ions, there are known ions of +1 charge and +2 charge. In the present invention, +1 charge copper ion compounds are mainly used, but it should be noted that use of +2 charge copper ion compounds is not excluded.

Further, FIGS. 3 to 11 show monodentate, bidentate or tridentate ligands as the constituents of the compounds used for the copper complexes of the present invention.

In the present invention, those metal coordination compounds are used which have the above monodentate, bidentate or tridentate ligands coordinated with copper. The above mentioned ligands include those of 0 charge and −1 charge, which are combined with copper of the +1 charge to give metal coordination compounds with an overall charge of 0 or +1. The +1 charge metal coordination compounds will have a counter anion, which is, however, not particularly limited as long as it is an ion of −1 charge such as ClO₄—, PF₆—, BF₄—, BPh₄-(tetra-phenylborate anion), or the like.

The synthesis of the above mentioned copper coordination compounds is described in the following documents. By following the synthesis examples shown therein, the copper coordination compounds of the present invention can easily be synthesized. For example, the compound examples shown in FIG. 12 can be synthesized by referring to the following papers.

-   Compound Example 1: Document 8 -   Compound Example 2: Document 7 -   Compound Example 3: Document 3 -   Compound Example 4: Document 4 -   Compound Example 5: Document 4 -   Compound Example 6: Document 9 -   Compound Example 7: Document 6 -   Compound Example 8: Document 4 -   Compound Example 9: Document 4 -   Compound Example 10: Document 10     [Synthesis Document] -   Document 1: D. Felder, et al., “Highly Luminescent     Cu(1)-Phenanthroline Complex in Rigid Matrix and Temperature     Dependence of the Photophysical Properties”, Journal of American     Chemical Society, 2001, 123, p 6299; -   Document 2: T. Shono, et al., “Syntheses of Copper(1)     Triphenylphosphine Complex”, Chemistry Letters, 1972, p 163; -   Document 3: M. T. Miller, et al., “Effects of Steric and Electronic     Delocalization on the Photophysical, Structural and Electrochemical     Properties of 2,9-Disubstituted 1,10-Phenanthroline Copper(1)     Complex”, Inorganic Chemistry, 1999, 38, p 3414; -   Document 4: R. A. Rader, et al., “Photostudies of [Cu(bpy)(PPh3)2]+,     [Cu(phen)(PPh3)2]+, and [Cu(dmp)(PPh3)2]+ in Solution and in Rigid,     Low Temperature Glasses, Simultaneous Multiple Emissions from     Intraligand and Charge Transfer States”, Journal of the American     Chemical Society, 1981, 103, p 5906; -   Document 5: R. M. Everly et al., “Reinvestigation of the Absorbing     and Emitting Charge-Transfer Excited States of [Cu(NN)2]+ Systems,     Journal of Physical Chemistry, 1991, 95, p 9071; -   Document 6: Whei-Lu Kwik et al., “Ternary Complexes of Copper (1)     with 2,9-Dimethyl-1,10-Phenanthroline and some Oxygen-doner     Ligands”, Journal of Chemical Society of Dalton; -   Document 7: M. T. Miller et al., “A Highly Emissive Heteroleptic     Copper(1) Bis(phenanthroline) Complex: [Cu(dbp)(dmp)]+”, Journal of     American Chemical Society, 1999, 121, p 4292; -   Document 8: M. K. Eggleston et al., “Steric Effects in Ground and     Excites States of Cu(NN)2+System”, Inorganic Chemistry, 1997, 36,     p172; -   Document 9: Arai et al., “Photocharacteristics of Copper (1) Complex     Containing Diphosphine and Diimine”,     Extended Abstracts (51th Complex Chemistry Forum), p 578, 2P-F13;     and -   Document 10: Kinoshita et al., “Development of Sulfur-Crosslinked     Large Ring Calix[4]pyridine and Novel Complex Group”, Extended     Abstracts (51th Complex Chemistry Forum), p 425, 2S3-06.

The present invention includes not only the ordinary organic copper complex compounds exemplified in FIG. 12 but also polymer compounds having a copper coordination moiety incorporated into the chain thereof such as shown in FIG. 13.

Tables 1 to 5 show compound examples of the metal complexes that can be used for the present invention. In the tables, the number in each of the columns of “Ligand 1” and “Ligand 2” means the number assigned for the ligands in FIGS. 3 to 11, and the blank in each of the columns of “Number of Ligand 1” and “Number of Ligand 2” means that the number is 1 (i.e., no indication of the number means 1).

TABLE 1 Number of Number of Compound No. Ligand 1 Ligand 1 Ligand 2 Ligand 2 1 511 511 2 510 55 3 515 515 4 55 1002 5 51 1001 2 6 55 1007 7 55 1002 8 510 1001 2 9 41 1001 2 10 1101 Iodine Ion 11 42 1001 2 12 43 1001 2 13 44 1001 2 14 45 1001 2 15 46 1001 2 16 47 1001 2 17 48 1001 2 18 49 1001 2 19 410 1001 2 20 411 1001 2 21 412 1001 2 22 413 1001 2 23 414 1001 2 24 41 1002 25 42 1002 26 43 1002 27 44 1002 28 45 1002 29 46 1002 30 47 1002 31 48 1002 32 49 1002 33 410 1002 34 411 1002 35 412 1002 36 413 1002 37 414 1002 38 41 1005 39 42 1005 40 43 1005 41 44 1005 42 45 1005 43 46 1005 44 47 1005 45 48 1005 46 49 1005 47 410 1005 48 411 1005 49 412 1005 50 413 1005 51 414 1005 52 51 56 53 52 56 54 53 56 55 54 56 56 55 56 57 56 56 58 57 56 59 58 56 60 59 56

TABLE 2 Number of Number of Compound No. Ligand 1 Ligand 1 Ligand 2 Ligand 2 61 510 56 62 511 56 63 512 56 64 513 56 65 514 56 66 51 510 67 52 510 68 53 510 69 54 510 70 55 510 71 57 510 72 58 510 73 59 510 74 510 510 75 511 510 76 512 510 77 513 510 78 514 510 79 51 58 80 52 58 81 53 58 82 54 58 83 55 58 84 57 58 85 58 58 86 59 58 87 510 58 88 511 58 89 512 58 90 513 58 91 514 58 92 51 514 93 52 514 94 53 514 95 54 514 96 55 514 97 56 514 98 57 514 99 59 514 100 511 514 101 512 514 102 513 514 103 514 514 104 51 1002 105 52 1002 106 53 1002 107 54 1002 108 55 1002 109 56 1002 110 57 1002 111 58 1002 112 59 1002 113 511 1002 114 512 1002 115 513 1002 116 514 1002 117 51 1005 118 52 1005 119 53 1005 120 54 1005

TABLE 3 Number of Number of Compound No. Ligand 1 Ligand 1 Ligand 2 Ligand 2 121 55 1005 122 56 1005 123 57 1005 124 58 1005 125 59 1005 126 511 1005 127 512 1005 128 513 1005 129 514 1005 130 51 1007 131 52 1007 132 53 1007 133 54 1007 134 55 1007 135 56 1007 136 57 1007 137 58 1007 138 59 1007 139 510 1007 140 511 1007 141 512 1007 142 513 1007 143 514 1007 144 51 1001 2 145 52 1001 2 146 53 1001 2 147 54 1001 2 148 55 1001 2 149 56 1001 2 150 57 1001 2 151 58 1001 2 152 59 1001 2 153 510 1001 2 154 511 1001 2 155 512 1001 2 156 513 1001 2 157 514 1001 2 158 61 1007 159 62 1007 160 63 1007 161 64 1007 162 65 1007 163 66 1007 164 67 1007 165 68 1007 166 69 1007 167 61 1001 2 168 62 1001 2 169 63 1001 2 170 64 1001 2 171 65 1001 2 172 66 1001 2 173 67 1001 2 174 68 1001 2 175 69 1001 2 176 71 1001 2 177 72 1001 2 178 73 1001 2 179 74 1001 2 180 75 1001 2

TABLE 4 Number of Number of Compound No. Ligand 1 Ligand 1 Ligand 2 Ligand 2 181 76 1001 2 182 77 1001 2 183 78 1001 2 184 79 1001 2 185 710 1001 2 186 71 1002 187 72 1002 188 73 1002 189 74 1002 190 75 1002 191 76 1002 192 77 1002 193 78 1002 194 79 1002 195 710 1002 196 81 1002 197 82 1002 198 83 1002 199 84 1002 200 85 1002 201 86 1002 202 87 1002 203 88 1002 204 89 1002 205 81 1005 206 82 1005 207 83 1005 208 84 1005 209 85 1005 210 86 1005 211 87 1005 212 88 1005 213 89 1005 214 91 1007 215 92 1007 216 93 1007 217 94 1007 218 95 1007 219 96 1007 220 97 1007 221 91 1001 2 222 92 1001 2 223 93 1001 2 224 94 1001 2 225 95 1001 2 226 96 1001 2 227 97 1001 2 228 91 57 229 92 57 230 93 57 231 94 57 232 95 57 233 96 57 234 97 57 235 111 2 1002 236 112 2 1002 237 113 2 1002 238 114 2 1002 239 115 2 1002 240 116 2 1002

TABLE 5 Number of Number of Compound No. Ligand 1 Ligand 1 Ligand 2 Ligand 2 241 111 2 1005 242 112 2 1005 243 113 2 1005 244 114 2 1005 245 115 2 1005 246 116 2 1005 247 111 2 1001 2 248 112 2 1001 2 249 113 2 1001 2 250 114 2 1001 2 251 115 2 1001 2 252 116 2 1001 2 253 31 2 1002 254 32 2 1002 255 33 2 1002 256 34 2 1002 257 35 2 1002 258 36 2 1002 259 37 2 1002 260 31 2 1007 261 32 2 1007 262 33 2 1007 263 34 2 1007 264 35 2 1007 265 36 2 1007 266 37 2 1007 267 31 2 1005 268 32 2 1005 269 33 2 1005 270 34 2 1005 271 35 2 1005 272 36 2 1005 273 37 2 1005 274 56 1008 275 510 1008 276 411 1008

The copper coordination compounds that can be utilized for the present invention are not limited to those mentioned above. For example, although FIGS. 8 and 9 illustrate only the main skeletal structures of the ligands, the hydrogen atom(s) thereof may be substituted with alkyl group(s), aromatic ring group(s), halogen atom(s), or the like. Further, they may have a fused ring structure or have CH group(s) thereof substituted with nitrogen atom(s).

A key feature of the copper coordination compounds preferably used in the present invention is that the nitrogen atom of a heterocyclic ring imine structure coordinates with Cu of +1 charge. The excited state of the copper coordination compounds having such a structure belongs to the so-called Metal-to-Ligand Charge Transfer (MLCT) excited state, so that a strong light emission can be obtained. In order to attain this excited state, it is preferable that the ligand has a large electron acceptance. For instance, in case of a bidentate ligand, both the two atoms of the ligand for coordination with the metal are nitrogen atoms with the imine structure. For this purpose, there can be employed, for example, 2,9-phenanthroline, 2,2′-bipyridine, and derivatives thereof. Further, in case of a monodentate ligand, pyridine derivatives can be employed.

In the present invention, it is especially preferable to adopt such a ligand structure as to suppress a structural change between a ground state and an excited state. The coordination structure of a copper complex in which the copper ion as a metal center is in +1 charge state (hereinafter referred to as “Cu(1)”) is a pseudo-tetrahedral structure of 4 coordinate, and it is preferable to maintain this structure also in an excited state in order to obtain a high light-emission luminance.

For example, in the case of Compound Example 1 shown in FIG. 12, each phenanthroline is substituted at positions 2 and 9 with two isobutyl groups. This exhibits an effect of maintain the pseudo-tetrahedral structure taken in a ground state also in an excited state to provide a high light-emission luminance. Although in an excited state the two phenanthrolines are liable to take a single planer configuration, the phenanthrolines can be substituted with bulky isobutyl groups to maintain the pseudo-tetrahedral structure. It is believed that Compound Examples 3-8 shown in FIG. 12 also exhibit high-luminance light emission characteristics on the basis of the same theory.

Further, the copper complexes used for the present invention, when compared with other commonly used light emitting materials, show not so higher light emission efficiencies in a solution but shows very strong light emission in a solid state of a film-shaped light emitting device. The possible reason for this phenomenon is as follows.

1. The coordination structure of Cu(1) in a ground state is the pseudo-tetrahedral structure of 4 coordinate. When the Cu(1) in the ground state are excited to be brought into an excited state, in order to form the MLCT excited state, the Cu becomes to have a charge near +2, so that taking a planer configuration becomes stable. This results in a great change in structure between the excited state and the ground state, so that thermal deactivation routes for energy increase to weaken the light emission. However, because this structural change is inhibited in a solid state, the suppression of the structural change would provide a strong light emission.

2. There is a possibility that in a solution, an additional coordination structure may be formed to form 5-coordinate structure, so that a strong light emission can not be obtained. Such 5-coordinate formation reaction is difficult to occur in a solid state because of the suppressed molecular motion, whereby a strong light emission can be obtained in a solid state.

Further, the Cu coordination compounds used for the present invention has a light emission lifetime of 0.1 μsec or more in a solid state. The longer the light emission lifetime, the fewer the thermal deactivation routes and the higher the light emission efficiency. Thus, the coordination compounds used for the present invention has a light emission lifetime of preferably 0.1 μsec or more, more preferably 0.5 μsec or more.

The hitherto used aluminoquinolinol derivatives, coumarin derivatives, quinacridone derivatives, and so on provide a strong light emission in a solution and the strong light emission characteristics are maintained also in a solid dispersion. The characteristics effectively function also in an organic EL device to provide a high light-emission efficiency of the device.

On the other hand, the Cu complexes used in the present invention have a unique property of providing a remarkably stronger light emission in a solid state than in a solution. The present inventors have found that this unique property is very useful for attaining a highly efficient, stable light emission of organic EL devices.

Further, the present invention can also be applied to polymer materials. For example, as shown in FIG. 13, a Cu coordination compound can be incorporated into a polymer chain to make the incorporated portion effectively function as a light emitting moiety.

The Cu coordination compounds in accordance with the present invention are useful as a light emitting material for organic EL devices. They have not only high light emission efficiencies but also properties suitable for film formation by vapor deposition or spin coating after dispersion into a polymer. Further, it becomes possible to stably produce EL devices without damages such as decomposition during device production steps. Moreover, it has been confirmed that EL devices produced using the Cu coordinating compounds pose no problem to light emission stability during current passing.

Further, as shown in examples as described below, durability tests by current passing have proved that the Cu coordination compounds in accordance with the present invention have an excellent performance in stability.

In application to a display, application to a system driven by use of a thin film transistor (TFT) drive circuit of active matrix type can be mentioned.

Moreover, the switching device used is not particularly limited and application is possible to single-crystal silicon substrates, MIM devices, amorphous silicon (a-Si) type devices, and so on.

The light emitting device of a high light emission efficiency of the present invention can be applied to those products which require energy saving or high luminance. Such application examples include a light source for displays, illumination apparatuses or printers, a backlight for liquid crystal display apparatuses, and so on. As an image display apparatus, a lightweight flat-panel display with energy saving performance and high visibility can be provided. As a light source for printers, the light emitting device of the present invention can be used as a substitution for a laser light source portion of laser beam printers currently used widely. An image can be formed by arranging the independently addressable devices of the present invention on an array and performing a desired exposure to a photosensitive drum. Using the device of the present invention makes it possible to greatly reduce the apparatus size. When it is utilized as a backlight of illumination apparatuses or liquid crystal displays, energy-saving effect can be expected.

As described above, Compounds Examples 1-10 of FIG. 12 were synthesized by referring to the documents. The molecular structures of the thus obtained compounds were identified by means of a mass spectrometer, NMR, or the like. As to the materials shown in Table 6 below of the compounds, light emission characteristics by photoexcitation was measured. The light emission spectrum was measured using Hitachi F4500 fluorescence spectrophotometer (excitation wavelength: 380-450 nm).

Further, the light emission lifetime was measured using model C4334 Streakscope manufactured by Hamamatsu Photonics Co. with a nitrogen laser light of wavelength 337.1 nm as an excitation light. All the measurements were carried out in a powder state. Moreover, the light emission spectrum was measured also for 5% by weight dispersion liquid of the compound in polymethyl methacrylate (PMMA) to obtain substantially the same spectrum as that for the compound powder.

TABLE 6 Light Emission Light Emission Compound Example Spectrum Peak Lifetime No. λmax (nm) τ (msec) 1 625 1 2 645 2.7 3 650 0.8 4 507 21.2 5 539 18.3 6 575 15 8 520 15 9 640 10 591 1.7

As a result, each compound example provided a strong light emission in the solid state.

EXAMPLES

In the following, the present invention will be further described by examples, but the present invention is not limited to such examples.

Example 1

An organic EL device was produced using Compound Example 4 as a light emitting material.

A device of a constitution having a single organic layer was produced. After forming an ITO film in a thickness of 100 nm on a glass substrate, the film was patterned such that each opposing area of upper and lower electrodes becomes 3 mm². Then, the following solution was prepared and applied by spin coating to the thus prepared ITO substrate.

(Solution)

-   Chlorobenzene: 10 g; -   Polyvinyl carbazole (Average molecular weight: 9600): 100 mg; and -   Compound Example 4: 3.0 mg

By performing spin coating using this solution at 2000 rpm for 20 seconds in a nitrogen atmosphere, an organic film of 120 nm in thickness could be obtained. After the film formation, the substrate was put in a vacuum vapor deposition chamber and a cathode of the following constitution was formed.

(Cathode)

-   Metal electrode layer 1 (15 nm): Al—Li alloy (Li content: 1.8% by     weight); and -   Metal electrode layer 2 (100 nm): Al

Then, a DC voltage was applied to the device with the Al electrode being a cathode and the ITO electrode being an anode to evaluate the device characteristics.

A result of measurement of the current-voltage characteristics showed that the device of this example prepared using Compound Example 4 had a good rectifying property. The light emission spectrum was measured with a spectrometer SR1 manufactured by TOPCON CORP. As is seen from the result shown in FIG. 14, the light emission spectrum peak is 545 nm, which is longer by about 40 nm than the PL (photoluminescence) spectrum peaks of the powder sample and the in-PMMA dispersed sample. The color of the emitted light was yellowish green by visual observation and stable light emission was maintained during continuous current passing for 200 hours. The light emission efficiency under application of a voltage of 10 V was calculated to be 0.5 lm/W.

Example 2

An organic EL device was produced following the same procedure as in Example 1, with the exception that Compound Example 1 was used as a light emitting material in place of Compound Example 4 used in Example 1. In this example, the light emission spectrum peak was 650 nm and a light emission of red color was observed. Stable light emission was maintained during continuous current passing for 200 hours.

Example 3

An organic EL device was produced following the same procedure as in Example 1, with the exception that Compound Example 8 was used as a light emitting material in place of Compound Example 4 used in Example 1. In this example, the light emission spectrum peak was 523 nm and a light emission of green color was observed. Stable light emission was maintained during continuous current passing for 200 hours.

Example 4

A light emitting material of a molecular structure having a Cu complex incorporated into a polymer was prepared.

First, a synthesis method will be described.

A Cu monomer metal complex compound for the present invention can be obtained via a synthesis pathway shown below.

Specifically, in a 100 ml 3-necked flask, 20 ml of acetonitrile and 0.54 g (5.45 mmole) of copper iodide were put in, 0.40 g (1.92 mmol) of 2,9-dimethyl-1,10-phenanthroline dissolved in 20 ml of hot ethanol was slowly added thereto in a stream of nitrogen, and the mixture was heated under reflux with stirring for 1 hour. Thereafter, 0.41 g (1.92 mmol) of 2-(acetacetyloxy)ethyl methacrylate dissolved in 10 ml of ethanol was slowly added thereto, and the mixture was heated under reflux for 24 hours. The reaction product was cooled with ice, and a precipitate was separated by filtration and washed with water. After the filtrate was removed under reduced pressure, purification was performed using a preparative HPLC manufactured by Nippon Bunsekikagaku K.K. to give the objective compound M1.

[Polymerization Reaction]

In a polymerization tube, 2 ml of N,N′-dimethyl formamide, 49 mg (0.1 mmol) of the compound M1, 174 mg (0.9 mmol) of VK (vinylcarbazole), and 1.64 mg (0.001 mmol) of AIBN (2,2′-azobis(isobutylonitrile)) were put in, and, after degassing and sealing, were heated under agitation for 20 hours at 60° C. After the reaction completed, the reaction mixture was re-precipitated three times from 100 ml of ether, and obtained powder was dried under heating at a reduced pressure to obtain the compound P1. The polymer compound had an average molecular weight of about 15,000. The molar ratio of the introduction rate of the compound M1 and VK was found to be about 1:29 by means of ¹H-NMR.

A 1% chloroform solution of this polymer compound was prepared and subjected to flow casting on a glass sheet, followed by measurement of photoluminescence spectrum using Hitachi F4500 fluorescence spectrophotometer with an excitation wavelength of 350 nm. The light emission peak wavelength was 560 nm, and a strong light emission was confirmed. The light emission lifetime at that wavelength was 0.5 μsec.

Example 5

A device of a constitution having a single organic layer was produced using the polymer coordination compound prepared in Example 4. A 1.1 mm thick, 5 cm square glass substrate with a transparent electrode ITO film was provided, and the ITO film was patterned in a predetermined shape. A 2% chloroform solution of the compound P1 was prepared and applied thereon by spin coating under the conditions of 2000 rpm for 20 seconds. Thereafter, drying was effected at 80° C. for 2 hours to obtain a polymer film of 120 nm in thickness. As an opposing electrode, a film consisting of a 10 nm thick Al—Li alloy layer and a 100 nm thick Al layer was formed by vapor deposition using a mask of a predetermined aperture pattern to form a light emitting device. When a DC voltage of 20 V was applied to the electrodes, the device emitted a light at an emission wavelength 570 nm, and stable light emission was maintained during continuous current passing for 200 hours.

Example 6

The compound obtained in Example 4 was employed in the preparation of a single-bit organic EL device the organic layer of which was constituted of the three layers, namely a hole transport layer, a light emitting layer and an electron transport layer as shown in FIG. 1B, and the characteristics of the device were measured.

An alkali-free glass substrate was employed as a transparent substrate 15, and, on the substrate, was formed indium tin oxide (ITO) in a thickness of 100 nm by sputtering as a transparent electrode 14 and was patterned into an electrode size of a diameter of 2 mm.

A hole transport layer 13 was formed thereon in a thickness of 30 nm by spin coating of a polymer film forming solution of a mixture of PEDOT and PSS represented by the foregoing chemical formulas. Then, a light emitting layer 12 was formed by two times of spin coating of a 1.0% chloroform solution of the polymer compound P1 of Example 4, followed by drying for 60 minutes in an oven of 60° C. to attain a film thickness of 70 nm. Then, an electron transport layer 16 was formed by resistance-heated evaporation of Bphen compound of the foregoing structure in vacuum of 10⁻⁴ Pa in a film thickness of 40 nm.

Then, potassium fluoride (KF) was provided in a thickness of 5 nm as an underlying layer for a metal electrode layer. Then, a metal electrode 11 was formed by evaporating an aluminum (Al) film of a thickness of 100 nm to form a cathode layer, whereby an organic EL device was prepared.

In order to investigate the characteristics of thus prepared organic EL device, the current-voltage characteristics were measured with a microammeter 4140B manufactured by Hewlett-Packard Co., and the luminance of light emission was measured by Model BM7 manufactured by TOPCON CORP. As a result, the device of this example prepared using Compound Example 4 showed a good rectifying property.

Further, a light emission from this EL device was confirmed under application of a voltage of 15 V. The light emission wavelength peak was 565 nm; substantially the same light emission wavelength as that of Example 5 was confirmed; and there was confirmed a light emission derived from the Cu coordination moiety of the polymer compound.

INDUSTRIAL APPLICABILITY

The present invention has been described in detail above with reference to the preferred embodiments and the examples. According to the present invention, by employing a copper complex as a light emitting material, it is possible to provide a light emitting device of a high light-emission luminance. Further, because the copper complexes are generally inexpensive, the light emitting device of the present invention can usefully be applied to display apparatuses and so on. 

1. A light emitting device comprising a pair of electrodes provided on a substrate and an organic substance layer provided between the electrodes, wherein the organic substance layer comprises a metal coordination compound represented by one of the following formulae:


2. The light emitting device according to claim 1, wherein the metal coordination compound has a light emission lifetime of 0.1 μsec or more.
 3. The light emitting device according to claim 1, wherein the metal coordination compound has a light emission lifetime of 0.5 μsec or more.
 4. A display apparatus comprising the light emitting device as set forth in claim 1 and an electrical signal application circuit for applying an electrical signal to drive the light emitting device. 